Bipolar plate with force concentrator pattern

ABSTRACT

Embodiments of present disclosure are directed to a bipolar plate assembly. The bipolar plate assembly has a frame and a base. At least one of the frame and the base has a shape of a force concentrator pattern or has a first surface having a force concentrator pattern, the force concentrator pattern including a raised surface extending partially across the first surface. A surface area of the force concentrator pattern across the length of the frame or base is generally constant, thereby producing a uniform compressive pressure along the length of the frame or base when the bipolar plate assembly is under compression.

This application claims the benefit of U.S. Provisional Application No.62/221,276, filed Sep. 21, 2015, which is incorporated by reference inits entirety.

The present disclosure is directed towards a bipolar plate, and moreparticularly, a bipolar plate having a force concentrator pattern.

Electrochemical cells, usually classified as fuel cells or electrolysiscells, are devices used for generating current from chemical reactions,or inducing a chemical reaction using a flow of current. A fuel cellconverts the chemical energy of a fuel (e.g., hydrogen, natural gas,methanol, gasoline, etc.) and an oxidant (air or oxygen) intoelectricity and waste products of heat and water. A basic fuel cellcomprises a negatively charged anode, a positively charged cathode, andan ion-conducting material called an electrolyte.

Different fuel cell technologies utilize different electrolytematerials. A Proton Exchange Membrane (PEM) fuel cell, for example,utilizes a polymeric ion-conducting membrane as the electrolyte. In ahydrogen PEM fuel cell, hydrogen atoms may electrochemically split intoelectrons and protons (hydrogen ions) at the anode. The electrons flowthrough the circuit to the cathode and generate electricity, while theprotons diffuse through the electrolyte membrane to the cathode. At thecathode, hydrogen protons may react with electrons and oxygen (suppliedto the cathode) to produce water and heat.

An electrolysis cell represents a fuel cell operated in reverse. A basicelectrolysis cell may function as a hydrogen generator by decomposingwater into hydrogen and oxygen gases when an external electric potentialis applied. The basic technology of a hydrogen fuel cell or anelectrolysis cell may be applied to electrochemical hydrogenmanipulation, such as, electrochemical hydrogen compression,purification, or expansion.

An electrochemical hydrogen compressor (EHC), for example, may be usedto selectively transfer hydrogen from one side of a cell to another. AnEHC may include a proton exchange membrane sandwiched between a firstelectrode (i.e., an anode) and a second electrode (i.e., a cathode). Agas containing hydrogen may contact the first electrode and an electricpotential difference may be applied between the first and secondelectrodes. At the first electrode, the hydrogen molecules may beoxidized and the reaction may produce two electrons and two protons. Thetwo protons are electrochemically driven through the membrane to thesecond electrode of the cell, where they are rejoined by two reroutedelectrons and reduced to form a hydrogen molecule. The reactions takingplace at the first electrode and second electrode may be expressed aschemical equations, as shown below.

First electrode oxidation reaction: H₂→2H⁺+2e ⁻

Second electrode reduction reaction: 2H⁺+2e ⁻→H₂

Overall electrochemical reaction: H₂→H₂

EHCs operating in this manner are sometimes referred to as hydrogenpumps. When the hydrogen accumulated at the second electrode isrestricted to a confined space, the electrochemical cell compresses thehydrogen or raises the pressure. The maximum pressure or flow rate anindividual cell is capable of producing may be limited based on the celldesign. To achieve greater compression or higher pressure, multiplecells may be linked in series to form a multi-stage EHC. In amulti-stage EHC the gas flow path, for example, may be configured so thecompressed output gas of the first cell may be the input gas of thesecond cell. Alternatively, single-stage cells may be linked in parallelto increase the throughput capacity (i.e., total gas flow rate) of anEHC. In both a single-stage and multi-stage EHC, the cells may bestacked and each cell may include a cathode, an electrolyte membrane,and an anode. Each cathode/membrane/anode assembly constitutes a“membrane electrode assembly”, or “MEA,” which is typically supported onboth sides by bipolar plates.

The bipolar plates may provide mechanical support to the EHCs, and mayphysically separate individual cells in a stack while electricallyconnecting them. The bipolar plates may also provide high pressurezones, where the reactant or the fuel, for example, hydrogen,accumulates. In addition, the bipolar plates may also act as currentcollectors/conductors, and may provide passages for the reactant or thefuel. Typically, bipolar plates are made from metals, for example,stainless steel, titanium, etc., and from non-metallic electricalconductors, for example, graphite.

Hydrogen compressors or hydrogen pumps typically have hydrogenaccumulated at the second electrode restricted to the high pressure zoneformed by the bipolar plates. In addition, the pressure of the highpressure zone may increase as more and more hydrogen is formed andaccumulated. To reduce the potential of hydrogen leaks and improvesafety and energy efficiency, the high pressure zone may be sealed byone or more seals between the bipolar plates. A compressive load may beapplied to the bipolar plates of an EHC or an EHC stack to compress theseals and create sealing of the high pressure zone. The seals mayinclude ring-shaped seals extending around the circumference of the highpressure zone and/or may include a polymeric film coated or laminated onthe surface of one or more of the bipolar plates.

Sufficient and generally even compressive pressure needs to be appliedto the seal between the bipolar plates. A minimum compressive pressureapplied may be greater than the yield strength of the material of theseal such that the material of the seal may deform and thereby create asealing surface. In some embodiments, the minimum compressive pressuremay be below the yield strength of the material. If the compressivepressure is not generally even or non-uniform across the sealingsurface, the minimum compressive pressure may not be applied to someareas on the sealing surface, which may result in leaking of thereactant or the fuel at those areas. Current options to prevent orreduce the potential of leaking due to non-uniform compressive pressureapplied to the seal include applying a higher compressive load to thebipolar plates to ensure the minimum compressive pressure is appliedacross the sealing surface. However, applying a higher compressive loadmay result in a higher compressive pressure not only on the sealingsurface, but also on places of the bipolar plates that have been appliedthe minimum compressive pressure and may not withstand a highercompressive pressure. Thus a higher compressive load may result inhigher requirement for the materials for the bipolar plates and/or othercomponents of the EHC or the EHC stack, including, for example, materialcompatibility, material strength, cost of material, cost ofmanufacturing, and ease of manufacturing. Therefore, there exists a needfor a bipolar plate assembly that allows for more uniform and/or evendistribution of compressive pressure across the sealing surface and/orthe bipolar plates.

One aspect of the present disclosure is directed to a bipolar plateassembly. The bipolar plate assembly may include a frame and a base. Atleast one of the frame and the base may have a shape of a forceconcentrator pattern or include a first surface. The first surface mayinclude a force concentrator pattern that may include a raised surfaceextending partially across the first surface. The surface area of theforce concentrator pattern across the length of the frame or base may begenerally constant, thereby producing a uniform compressive pressurealong the length of the frame and/or base when the bipolar plateassembly is under compression.

Another aspect of the present disclosure is directed to a method ofcompressing a bipolar plate. The method may include compressing a frameand a base of the bipolar plate assembly. At least one of the frame andthe base may have a shape of a force concentrator pattern or may includea first surface. The first surface may include a force concentratorpattern that may include a raised surface extending partially across thefirst surface. The surface area of the force concentrator pattern acrossthe length of the frame or base may be generally constant. The methodmay further include producing a uniform compressive pressure along thelength of the frame and/or base when the bipolar plate assembly is undercompression.

Another aspect of the present disclosure is directed to anelectrochemical cell. The electrochemical cell may include a pair ofbipolar plates and a membrane electrode assembly located between thepair of bipolar plates. At least one of the bipolar plates may have ashape of a force concentrator pattern or may include a first surface.The first surface may include a force concentrator pattern that mayinclude a raised surface extending partially across the first surface.The surface area of the force concentrator pattern across the length ofthe frame or base may be generally constant. The method may furtherinclude producing a uniform compressive pressure along the length of theframe and/or base when the bipolar plate assembly is under compression.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory onlyand are not restrictive of the disclosure, as claimed.

The accompanying drawings, which are incorporated in and constitute apart of this specification, illustrate embodiments of the presentdisclosure and together with the description, serve to explain theprinciples of the disclosure.

FIG. 1 is an exploded side view of part of an electrochemical cell,showing various components of an electrochemical cell, according to anexemplary embodiment.

FIG. 2 is a perspective view of a base and a frame of a bipolar plateassembly, according to an exemplary embodiment.

FIG. 3 is a perspective view of a base and a frame of a bipolar plateassembly, according to an exemplary embodiment.

FIG. 4 is a top view of a frame of an exemplary bipolar plate assembly.

FIG. 5 is a top view of a frame of an exemplary bipolar plate assembly.

FIG. 6 is a perspective view of a frame of a bipolar plate assembly,according to an exemplary embodiment.

FIG. 7 is a close up view of a frame of a bipolar plate assembly,according to an exemplary embodiment.

FIG. 8 is a perspective view of a base and a frame of a bipolar plateassembly, according to an exemplary embodiment.

FIG. 9 is a top view of a frame of a bipolar plate assembly, accordingto an exemplary embodiment.

FIG. 10 is a perspective view of a frame of a bipolar plate assembly,according to an exemplary embodiment.

Reference will now be made in detail to the present exemplaryembodiments of the present disclosure, examples of which are illustratedin the accompanying drawings. Wherever possible, the same referencenumbers will be used throughout the drawings to refer to the same orlike parts. Although described in relation to an electrochemical cellfor compressing hydrogen, it is understood that the devices and methodsof the present disclosure may be employed with various types of fuelcells and electrochemical cells, including, but not limited toelectrolysis cells, hydrogen purifiers, hydrogen expanders, and hydrogenpumps.

FIG. 1 shows an exploded side view illustration of an electrochemicalcell 100, according to an exemplary embodiment. Electrochemical cell 100may include an anode 110, a cathode 120, and a proton exchange membrane(PEM) 130 disposed between anode 110 and cathode 120. Anode 110, cathode120, and PEM 130 combined may include a membrane electrode assembly(MEA) 140. PEM 130 may include a pure polymer membrane or compositemembrane where other material, for example, silica, heteropolyacids,layered metal phosphates, phosphates, and zirconium phosphates may beembedded in a polymer matrix. PEM 130 may be permeable to protons whilenot conducting electrons. Anode 110 and cathode 120 may include porouscarbon electrodes containing a catalyst layer. The catalyst material,for example, platinum, may increase the reaction of the reactant or thefuel.

Electrochemical cell 100 may further include two bipolar plates 150,160. Bipolar plates 150, 160 may act as support plates, conductors,provide passages to the respective electrode surfaces for the reactantor the fuel, and provide passages for the removal of the compressedreactant or fuel. Bipolar plates 150, 160 may also include accesschannels for cooling fluid (i.e., water, glycol, or water glycolmixture). Bipolar plates 150, 160 may separate electrochemical cell 100from the neighboring cells in an electrochemical stack (not shown). Insome embodiments, bipolar plate 150 and/or 160 may function as thebipolar plates for two neighboring cell such that each side of bipolarplate 150 and/or 160 is in contact with a different MEA 140. Forexample, multiple electrochemical cells 100 may be linked in series toform a multi-stage electrochemical hydrogen compressor (EHC) or stackedin parallel to form a single-stage EHC.

In operation, according to an exemplary embodiment, hydrogen gas may besupplied to anode 110 through bipolar plate 150. An electric potentialmay be applied between anode 110 and cathode 120, wherein the potentialat anode 110 is greater than the potential at cathode 120. The hydrogenat anode 110 may be oxidized causing the hydrogen to split intoelectrons and protons. The protons are electrochemically transported or“pumped” through PEM 130 while the electrons are rerouted around PEM130. At cathode 120 on the opposite side of PEM 130 the transportedprotons and rerouted electrons are reduced to form hydrogen. As more andmore hydrogen is formed at cathode 120 the hydrogen may be compressedand pressurized within a high pressure zone created in bipolar plate160.

In some embodiments, each of bipolar plates 150 and 160 may be formed oftwo pieces or components. For example, FIG. 2 shows one embodiment of atwo-component bipolar plate 160, wherein bipolar plate 160 includes aframe 170 and a base 180. Frame 170 may define a void 190 in fluidcommunication with a flow structure of base 180 (not shown). In someembodiments, frame 170 and base 180 may be formed as one integrated partor component. Although the following description references bipolarplate 160, such disclosure may be equally applicable to bipolar plate150.

Frame 170 and base 180 may be generally planar and have a generallyrectangular or elongated profile. In some embodiments, frame 170 andbase 180 may have another shape, for example, a square, a “race-track”(i.e., a substantially rectangular shape with semi-elliptical lateralsides), circle, oval, elliptical, or other shape. The shape of frame 170and base 180 may correspond to the other components of electrochemicalcell 100 (e.g., cathode, anode, PEM, flow structure, etc.) orelectrochemical cell stack.

Frame 170 and base 180 may be configured for coplanar coupling. Frame170 and base 180 may be releasably coupled or fixed together, or may beone integrated part. One or more attachment mechanisms may be usedincluding, for example, bonding material, welding, brazing, soldering,diffusion bonding, ultrasonic welding, laser welding, stamping,riveting, resistance welding, and/or sintering. In some embodiments, thebonding material may include an adhesive. Suitable adhesives include,for example, glues, epoxies, cyanoacrylates, thermoplastic sheets(including heat bonded thermoplastic sheets) urethanes, anaerobic,UV-cure, and other polymers. In some embodiments, frame 170 and base 180may be coupled by friction fit. For example, one or more seals betweenthe components may produce adequate frictional force between thecomponents when compressed to prevent unintended sliding.

In some embodiments, frame 170 and base 180 may be releasably coupledusing fasteners, for example, screws, bolts, clips, or other similarmechanisms. In some embodiments, compression rods and nuts may passthrough bipolar plates 150 and 160 or along the outside and be used tocompress frame 170 and base 180 together as electrochemical cell 100 ora plurality of electrochemical cells 100 are compressed in a stack.

In some embodiments, frame 170 and base 180 may help define a pluralityof different pressure zones, for example, a plurality of seals maydefine one or more different pressure zones. The plurality of differentseals and pressure zones, according to one embodiment are shown in FIG.2. The plurality of seals may include a first seal 240, a second seal250, and a third seal 260. First seal 250 may be contained entirelywithin second seal 250, and second seal 250 may be contained entirelywithin third seal 260. This arrangement of seals (i.e., one within theother) may be classified as a cascade seal configuration. The cascadeseal configuration may provide several advantages. For example, thecascade seal configuration may limit the potential of high pressurehydrogen escaping electrochemical cell 100 by providing seal redundancyin the form of multiple layers of sealing protection. Reducing thepotential of hydrogen leaks may benefit safety and energy efficiency. Inaddition, the cascade seal configuration may also allow forself-regulation of pressure by allowing the bleeding of high pressurefrom high pressure zones to lower pressure zones.

The shape of first seal 240, second seal 250, and third seal 260 maygenerally correspond to the shape of bipolar plates 150 and 160, asshown in FIG. 2. First seal 240, acting as a high pressure seal, maydefine a portion of a high pressure zone 200 and be configured tocontain a first fluid 212 (e.g., hydrogen) within high pressure zone200. First seal 240 may delimit the outer boundaries of high pressurezone 200 at least between frame 170 and base 180. High pressure zone 200may be configured to contain at least one flow structure (not shown),for example, a cathode flow structure and an anode flow structure,extending through void 190 when frame 170 and base 180 are coupled orwhen frame 170 and base 180 are formed as one integrated piece.

First fluid 212, such as hydrogen, may be formed at cathode 120 andaccumulate at high pressure zone 200 and the connection between frame170 and base 180 may be sealed by first seal 240. Hydrogen within highpressure zone 200 may be compressed and, as a result, may increase inpressure as more and more hydrogen is formed and collected in highpressure zone 200. Hydrogen in high pressure zone 200 may be compressedto a pressure greater than, for example, about 10,000 psig, about 15,000psig, about 20,000 psig, about 25,000 psig, about 30,000 psig, or about35,000 psig.

As shown in FIG. 2, first seal 240 may be configured to extend aroundthe exterior of high pressure ports 210. High pressure ports 210 may beconfigured to supply or discharge first fluid 212 from high pressurezone 200. High pressure ports 210 may be in fluid communication withhigh pressure ports of adjacent electrochemical cells in a multi-cellelectrochemical compressor. High pressure ports 210 may be in fluidcommunication with the cathode flow structure (not shown), which may belocated on top of base 180 extending through void 190.

In some embodiments, second seal 250 may define the outer circumferenceof an intermediate pressure zone 202. Intermediate pressure zone 202 maybe delimited by first seal 240, second seal 250, frame 170, and base180. As shown in FIG. 2, intermediate pressure zone 202 may extendaround the circumference of high pressure zone 200 separated by firstseal 240. Intermediate pressure zone 202 may be configured to contain asecond fluid 214. The cross-sectional area and volume of intermediatepressure zone 202 may vary based on the geometry of frame 170, base 180,first seal 240, and second seal 250. Intermediate pressure zone 202 mayfurther include and be in fluid communication with one or moreintermediate pressure ports 220. Intermediate pressure ports 220 may beconfigured to discharge second fluid 214 contained within intermediatepressure zone 202. Intermediate pressure ports 220 may be in fluidcommunication with the anode flow structure (not shown), which may belocated on top of the cathode flow structure extending through void 190.

The shape and number of intermediate pressure ports 220 may vary. Forexample, intermediate pressure ports 220 may be square, rectangle,triangle, polygon, circle, oval, or other shape. The number ofintermediate pressure ports 220 may vary from 1 to 25 or more. As shownin FIG. 2, intermediate pressure ports 220 may be evenly distributedalong the length of frame 170 and base 180 of bipolar plate 160. In someembodiments, intermediate pressure ports 220 may extend the fullcircumference of intermediate pressure zone 202.

In some embodiments, second fluid 212 discharged via intermediatepressure ports 220 may be resupplied to electrochemical cell 100. Insome embodiments, second fluid 214 discharged via intermediate pressureports 220 may be collected and recycled. Second fluid 214 inintermediate pressure zone 202 may generally have lower pressure thanfirst fluid 212 in high pressure zone 200.

In some embodiments, third seal 260 may define low pressure zone 204 andbe configured to contain a third fluid 216 within low pressure zone 204.Low pressure zone 204 may be delimited by second seal 250, third seal260, frame 170, and base 180. As shown in FIG. 2, low pressure zone 204may extend around the circumference of intermediate pressure zone 202,separated by second seal 240. The cross-sectional area and volume of lowpressure zone 204 may vary based on the geometry of frame 170, base 180,second seal 240, and third seal 250. Low pressure zone 204 may furtherinclude and be in fluid communication with one or more low pressureports 230. Low pressure ports 230 may be configured to discharge thirdfluid 216 collected and/or contained within low pressure zone 204.

The shape and number of low pressure ports 230 may vary. For example,low pressure ports 230 may be square, rectangle, triangle, polygon,circle, oval, or other shape. The number of low pressure ports 230 mayvary, for example, from 1 to 50 or more. As shown in FIG. 2, lowpressure ports 230 may be spaced between second seal 240 and third seal250 and evenly distributed along the length of bipolar plate 160. Insome embodiments, low pressure ports 230 may extend the fullcircumference of low pressure zone 204.

In some embodiments, third fluid 216 discharged via low pressure ports230 may be resupplied to electrochemical cell 100. In some embodiments,third fluid 216 discharged via low pressure ports 230 may be collectedand recycled. Third fluid 216 in low pressure zone 204 may generallyhave lower pressure than first fluid 212 in high pressure zone 200 andsecond fluid 214 in intermediate pressure zone 202.

According to exemplary embodiments, first seal 240, second seal 250, andthird seal 260 may be part of an assembly of sealing components capableof sealing different pressure zones (e.g., high pressure zone 200,intermediate pressure zone 202, and low pressure zone 204) of bipolarplate 160, and withstanding pressures in excess of about 15,000 psig,about 20,000 psig, about 25,000 psig, about 30,000 psig, about 35,000psig, about 40,000 psig, or greater than about 40,000 psig for longperiods of time (e.g., greater than 10 years) and withstand manypressure cycles (e.g., greater than 1,000 cycles). For example, firstseal 240 may be capable of sealing high pressure zone 200 having apressure ranging from about 25,000 psig to about 40,000 psig, secondseal 250 may be capable of sealing intermediate pressure zone 202 havinga pressure ranging from about 0 psig to about 3,000 psig, and third seal260 may be capable of sealing low pressure zone 204 having a pressureranging from about 0 psig to about 20 psig.

In some embodiments, bipolar plates 150 and 160 may be configured suchthat just two pressure zones are formed. For example, bipolar plates 150and 160 may be configured such that just first seal 240 and third seal260 form high pressure zone 200 and low pressure zone 204, therebyeliminating second seal 250 and intermediate pressure zone 202. In someembodiments, it is also contemplated that bipolar plates 150 and 160 maybe configured such that more than three pressure zones are formed. Forexample, a fourth pressure zone may be formed by adding a fourth seal.

Traditionally, elastomer seals (e.g., O-rings) are used for first seal240, second seal 250, and/or third seal 260, for sealing high pressurezone 200, intermediate pressure zone 202, and/or low pressure zone 204created between frame 170 and base 180 and for sealing high pressureports 210. Elastomers are often a reliability issue in a high pressuresystem. In addition to making the electrochemical cell less robust andtolerant, elastomeric seals need to be either die cut, hand placed,over-molded, or deposited using an x-y table and then cured. Further,elastomer seals may require either frame 170 or base 180 to have glandsor grooves on the surface. Although elastomer seals can be bonded intothe grooves, they may slip out of place during fabrication, assembly,and/or during operation. Due to the unreliability and complication ofthe fabrication process caused by elastomer seals, in some embodiments,polymeric seals may be advantageously used for sealing at least one ofthe pressure zones formed between frame 170 and base 180.

Polymeric seals can be applied to frame 170 and/or base 180 by a varietyof techniques, for example, laminating, spray coating, or dip coating.Utilizing polymeric seals may allow the complexity of bipolar plates150, 160 to be reduced. For example, glands or grooves on the surfacesof frame 170 and/or base 180 may be eliminated. Eliminating the glandsor grooves may allow frame 170 and/or base 180 to be thinner, reduce theamount of machining and/or fabrication required, and increase the areaof a sealing surface between frame 170 and base 180, which may reducethe compressive pressure that frame 170 and/or base 180 need towithstand. For another example, using polymeric seals may allow frame170 and base 180 to be formed as one integrated piece, which may furtherreduce the thickness of bipolar plates 150, 160. In addition, laminatedor spray coated polymeric seals may be tightly bonded to frame 170and/or base 180 and thus may be firmly held in place. Polymeric sealsmay allow lower cost of fabrication due to less machining of the bipolarplates 150 and 160, lower application cost, and reduced material of thebipolar plates 150 and 160.

As shown in FIG. 3, a polymeric seal 175, for example, may be laminatedor coated on one or both surfaces or frame 170 and/or base 180. When acompressive load is applied to frame 170 and base 180, polymeric seal175 may deform and seal high pressure zone 200, intermediate pressurezone 202, and/or low pressure zone 204. Polymeric seal 175 may beconfigured, for example, to aid in containing first fluid 212 withinhigh pressure zone 200, containing second fluid 214 within intermediatepressure zone 202, an/or containing third fluid 216 within low pressurezone 204. In some embodiments, polymeric seal 175 may cover part or allof the surface area of frame 170 and/or base 180. Polymeric seal 175 mayhave a sealing surface extending across a compressed area between frame170 and base 180, and may extend around the circumferences of highpressure zone 200, intermediate pressure zone 202, and/or low pressurezone 204.

In some embodiments, polymeric seal 175 may be used in place of firstseal 240, second seal 250, and/or third seal 260. For example, as shownin FIG. 4, polymeric seal 175 may be used together with first seal 240sealing high pressure zone 200 and polymeric seal 175 sealing theintermediate pressure zone 202 and low pressure zone 204. In someembodiments, one or more channels may form between intermediate pressureports 220 and high pressure zone 200, allowing intermediate pressureports 220 to be in fluid communication with first seal 240, highpressure zone 200, and/or the anode flow structure (not shown).Polymeric seal 175 may also include one or more channels 178 to allowintermediate pressure ports 220 to be in fluid communication with highpressure zone 200.

In some embodiments, polymeric seal 175 may be capable of sealingdifferent pressure zones and withstand pressures in excess of about15,000 psig, about 20,000 psig, about 25,000 psig, about 30,000 psig,about 35,000 psig, or about 40,000 psig, for long periods of time (e.g.,greater than 10 years) and withstand many pressure cycles (e.g., greaterthan 1,000 cycles). For example, polymeric seal 175 may be capable ofsealing high pressure zone 200 having a pressure ranging from about25,000 psig to about 40,000 psig, sealing intermediate pressure zone 202having a pressure ranging from about 0 psig to about 3,000 psig, and/orsealing low pressure zone 204 having a pressure ranging from about 0psig to about 20 psigg. This allows the reactant or the fuel, such ashydrogen, formed at cathode 120 to be highly compressed in, for example,high pressure zone 200.

The dimensions of polymeric seal 175 including the shape, thickness, andwidth may vary, and may be based on the dimensions of electrochemicalcell 100 and bipolar plate 160. The thickness of polymer seal 175 mayrange, for example, from about 0.01 mm to about 0.025 mm, from about0.025 mm to about 0.05 mm, from about 0.05 mm to about 0.1 mm, fromabout 0.1 mm to about 0.2 mm, from about 0.2 mm to about 0.3 mm, fromabout 0.025 mm to about 0.1 mm, from about 0.025 mm to about 0.2 mm,from about 0.025 mm to about 0.254 mm, from about 0.025 mm to about 0.3mm, from about 0.05 mm to about 0.1 mm, from about 0.05 mm to about 0.2mm, from about 0.05 mm to about 0.3 mm, from about 0.1 mm to about 0.2mm, or from about 0.1 mm to about 0.3 mm. In some embodiments, polymericseal 175 may be a separate thin polymeric film sandwiched between frame170 and base 180. In some embodiments, polymeric seal 175 may be coatedor laminated on either frame 170 or base 180 or on both frame 170 andbase 180. In some embodiments, polymeric seal 175 may be applied to thesurface of frame 170 that face base 180 and/or the surface of base 180that face frame 170. In some embodiments, polymeric seal 175 may beapplied to the surface of frame 170 facing a base 180 of an adjacentcell and/or may be applied to the surface of base 180 facing a frame 170an adjacent cell. In some embodiments, polymeric seal 175 may be appliedto both surfaces of frame 170 and/or base 180. In some embodiments,frame 170 may be formed by the material of polymeric seal 175 such thatthe range of the thickness of polymeric seal 175 is substantially thesame as that of frame 170.

In some embodiments, first seal 230, second seal 240, and/or third seal250 may be made of or be replaced by polymeric seal 175, as describedherein. In some embodiments, polymeric seal 175 may be used togetherwith first seal 240, second seal 250, and/or third seal 260. In someembodiments, polymeric seal 175, first seal 240, second seal 250, and/orthird seal 260 may be made of a polymeric sealing material including,but not limited to, Teflon™, Torlon®, polyether ether ketone (PEEK),polyethyleneimine (PEI), polyethylene terephthalate (PET), polycarbonate(PC), polyimide, and polysulfone. The polymer materials may be acidresistant and may not leach materials that are harmful to the operationof electrochemical cell 100. In some embodiments, frame 170 and/or base180 may be coated with an adhesive configured to aid in sealing. Theadhesive may be, for example, a pressure or heat activated adhesive

When bipolar plate 160 is assembled, frame 170 and base 180 (not shownin FIG. 4) may be joined and compressive pressure may be applied toframe 170, base 180, and polymeric seal 175 applied to frame 170 and/orbase 180. In some embodiments, a minimum compressive pressure appliedmay be greater than the yield strength of the material of polymeric seal175 such that the material of polymeric seal 175 may deform and therebycreate a sealing surface. In some embodiments, a minimum compressivepressure applied may not need to be greater than the yield strength ofthe material of polymeric seal 175 when the surface of frame 170 and/orbase 180 that polymeric seal 175 is applied to are substantiallypolished and a sealing surface may be created. The sealing surface maybe formed at a compressed area of frame 170 and/or base 180. Althoughthe following description references frame 170, such disclosure may beequally applicable to base 180.

As shown in FIG. 4, for example, the compressed area of frame 170 mayextend across a top surface of frame 170. In some embodiments, frame 170may have an elongated shape with a first end 171, a second end 172, andan elongated body 173 extending therebetween. In some embodiments, asshown in FIG. 4, first end 171 and second end 172 of frame 170 may havewider areas compared to elongated body 173, the compressed area alongelongated body 173 of frame 170 may be narrower or smaller than thecompressed area at first end 171 and second end 172 of frame 170. When acompressive load is applied to the compressed area of frame 170, thecompressed area at first end 171 and second end 172 of frame 170 mayundergo a smaller compressive pressure due to the difference in contactarea than the compressed area along elongated body 173 of frame 170.Such a situation may result in non-uniform compressive pressure acrossthe compressed area of frame 170 and the sealing surface of polymericseal 175. This may cause leaking of fluid at some places along thesealing surface, such as the places near first end 171 and second end172 where the compressive pressure may be less and in some situation maynot meet the minimum compressive pressure.

FIG. 5 shows an example when non-uniform compressive pressure is appliedto the compressed area of frame 170 and the sealing surface of polymericseal 175. The magnitude of the compressive pressure is shown in densityof diagonal lines. As shown in FIG. 5, the compressive pressure appliedat second end 172 of frame 170 is smaller than that applied to elongatedbody 173 of frame 170. In this example, if a minimum compressivepressure is applied to the compressed area along elongated body 173 offrame 170, a compressive pressure smaller than the minimum compressivepressure may then be applied to the compressed area at second end 172 offrame 170, posing potential risks, for example, of fluid leaking fromhigh pressure zone 200 to intermediate pressure zone 202, leaking fromintermediate pressure zone 202 to low pressure zone 204 or to theexternal of the bipolar plate, and/or leaking from low pressure zone 204to the external of the bipolar plate. Alternatively, if a compressivepressure applied to the compressed area at second end 172 of frame 170is equal to or sufficiently higher than a minimum compressive pressure,then the compressive pressure applied to the compressed area alongelongated body 173 of frame 170 may substantially exceed the maximumcompressive pressure that the material of frame 170 can withstand, whichmay necessitate higher design requirement and/or overdesign of frame 170to accommodate the excessive compressive pressure.

To increase the uniformity of compressive pressure applied to thecompressed area of frame 170 and/or base 180 and the sealing surface ofpolymeric seal 175, frame 170 and/or base 180 may define a forceconcentrator pattern 300. As shown in FIG. 6, force concentrator pattern300 may be a surface raised from a top and/or a bottom surface of frame170 and/or base 180. For example, force concentrator pattern 300 may begenerated by chemically etching or machining the top surface of frame170. In some embodiments, force concentrator pattern 300 may begenerated by machining frame 170 and/or base 180 to remove materials offrame 170 and/or base 180 such that the surface profile of frame 170and/or base 180 may be substantially the same as force concentratorpattern 300. For example, some materials of frame 170 near first end 171and second end 172 may be removed or etched away to generate forceconcentrator pattern 300. Although the following description referencesto force concentrator pattern 300 as a raised surface, such disclosuremay be equally applicable to force concentrator pattern 300 assubstantially same as the profile of frame 170 and/or base 180.

As shown in FIG. 7, for example, force concentrator pattern 300 may bedescribed as a raised surface 300′ above the top surface of frame 170.In such embodiments, polymeric seal 175 may be laminated or coated onforce concentrator pattern 300. In such embodiments, force concentratorpattern 300 may be formed by polymeric seal 175. In some embodiments,force concentrator pattern 300 may have a thickness, for example, fromabout 0.01 mm to about 0.025 mm, from about 0.025 mm to about 0.05 mm,from about 0.05 mm to about 0.1 mm, from about 0.1 mm to about 0.2 mm,from about 0.2 mm to about 0.3 mm, from about 0.025 mm to about 0.1 mm,from about 0.025 mm to about 0.2 mm, from about 0.025 mm to about 0.254mm, from about 0.025 mm to about 0.3 mm, from about 0.05 mm to about 0.1mm, from about 0.05 mm to about 0.2 mm, from about 0.05 mm to about 0.3mm, from about 0.1 mm to about 0.2 mm, or from about 0.1 mm to about 0.3mm. In some embodiments, force concentrator pattern 300 may be on eitherframe 170 or base 180 or on both frame 170 and base 180. In someembodiments, force concentrator pattern 300 may be on the surface offrame 170 that face base 180 and/or the surface of base 180 that faceframe 170. In some embodiments, force concentrator pattern 300 may be onthe surface of frame 170 facing a base 180 of an adjacent cell and/ormay be applied to the surface of base 180 facing a frame 170 an adjacentcell. In some embodiments, force concentrator pattern 300 may be on bothsurfaces of frame 170 and/or base 180. In some embodiments, thethickness of force concentrator pattern 300 may be substantially thesame as that of frame 170 and/or base 180.

As shown in FIG. 6 and FIG. 7, in some embodiments, force concentratorpattern 300 may extend across elongated body 173 of frame 170 andpartially across first end 171 and/or second end 172 of frame 170. Forceconcentrator pattern 300 may be designed such that the compressed areaacross frame 170, for example, across the length of frame 170, may beapproximately or generally constant or uniform. In some embodiments,force concentrator pattern 300 may extend from high pressure zone 200 tothe outer edge of frame 170. In some embodiments, force concentratorpattern 300 may be narrower than a width of elongated body 173 of frame170. For example, force concentrator pattern 300 may or may not extendfrom the inner edge of frame 170 to the outer edge of frame 170. In someembodiments, the compressed area of frame 170, the surface area of forceconcentrator pattern 300, and the surface area of the sealing surface ofpolymeric seal 175 may be substantially the same. The design of forceconcentrator pattern 300 may allow the compressive pressure across thecompressed area of frame 170 and the sealing surface of polymeric seal175, to be generally uniform or constant. In some embodiments,decreasing the surface area of force concentrator pattern 300, forexample, in first end 171 and/or second end 172, may increase theuniformity or evenness of the compressive pressure across the compressedarea of frame 170 and the sealing surface of polymeric seal 175.

FIG. 8 shows an exemplary embodiment of bipolar plate 160 whose frame170 has a force concentration pattern 300. When a compressive load isbeing applied to frame 170 and/or base 180, the compressive pressureapplied may be generally uniformly distributed across force concentratorpattern 300 of frame 170, the compressed area of frame 170, and/or thesealing surface of polymeric seal 175. The compressed area along thelength of frame 170 may range from about 2 cm²/cm to about 4 cm²/cm,from about 2 cm²/cm to about 6 cm²/cm, from about 2 cm²/cm to about 8cm²/cm, from about 2 cm²/cm to about 10 cm²/cm, from about 4 cm²/cm toabout 6 cm²/cm, from about 4 cm²/cm to about 8 cm²/cm, from about 4cm²/cm to about 10 cm²/cm, from about 5 cm²/cm to about 7 cm²/cm, fromabout 6 cm²/cm to about 8 cm²/cm, from about 6 cm²/cm to about 10cm²/cm. In some embodiments, a repeating distance between intermediateports 220 and/or low pressure ports 230 may range from about 1 cm toabout 3 cm. In some embodiments, the length of frame 170 and/or base 180may range from about 15 cm to about 30 cm, from about 15 cm to about 50cm, from about 15 cm to about 80 cm, from about 15 cm to about 100 cm,from about 30 cm to about 50 cm, from about 30 cm to about 80 cm, fromabout 30 cm to about 100 cm, from about 50 cm to about 80 cm, from about50 cm to about 100 cm, or from about 80 cm to about 100 cm. In someembodiments, the width of frame 170 and/or base 180 may range from about5 cm to about 10 cm, from about 10 cm to about 20 cm, from about 20 cmto about 30 cm, from about 5 cm to about 20 cm, from about 5 cm to about30 cm, from about 10 cm to about 30 cm, or from about 20 cm to about 30cm.

In some embodiments, the compressed area of frame 170, the surface areaof force concentrator pattern 300, and/or the surface area of thesealing surface of polymeric material 175 may range from about 50 cm² toabout 100 cm², from about 100 cm² to about 200 cm², from about 200 cm²to about 300 cm², from about 300 cm² to about 400 cm², from about 400cm² to about 500 cm², from about 500 cm² to about 600 cm², from about600 cm² to about 700 cm², from about 700 cm² to about 800 cm², fromabout 800 cm² to about 900 cm², from about 900 cm² to about 1000 cm²,from about 1000 cm² to about 1100 cm², from about 1100 cm² to about 1200cm², from about 1200 cm² to about 1300 cm², from about 1300 cm² to about1400 cm², or from about 1400 cm² to about 1500 cm². In some embodiments,the generally uniform compressive pressure distributed along thecompressed area of frame 170 and/or the sealing surface of polymericseal 175 may range from about 5,000 psig to about 10,000 psig, fromabout 5,000 psig to about 20,000 psig, from about 5,000 psig to about30,000 psig, from about 5,000 psig to about 40,000 psig, from about10,000 psig to about 40,000 psig, from about 10,000 psig to about 30,000psig, from about 10,000 psig to about 20,000 psig, from about 20,000psig to about 30,000 psig, from about 20,000 psig to about 40,000 psig,or from about 30,000 psig to about 40,000 psig.

FIG. 9 illustrates an example when generally uniform compressivepressure is distributed across the compressed area of frame 170 and thesealing surface of polymeric seal 175, when utilizing force concentratorpattern 300 as described herein. The magnitude of the compressivepressure is shown in density of diagonal lines. The uniform density ofthe diagonal lines in FIG. 9 indicates that the magnitude of compressivepressure across the compressed area of frame 170 is generally uniform.As shown in FIG. 9, force concentrator pattern 300 reduces thecompressed area at first end 171 of frame 170, and thus allows thecompressed area extending across first end 171 and elongated body 173 offrame 170 to be approximately constant, resulting in generally uniformor even distribution of the compressive pressure cross the compressedarea of frame 170 and the sealing surface of polymeric seal 175. In someembodiments, for example, given a compressive load of about 1,000,000pounds, the area of force concentrator pattern 300 and the compressivearea of frame 170 may be about 50 in², and thus the compressive pressuremay be about 20,000 psig across frame 170. This substantially uniform oreven distribution of compressive pressure may reduce or prevent thepotential of fluid leaking from high pressure zone 200. In someembodiments, the variability of compressive pressure cross thecompressed area of frame 170 and/or the sealing surface of polymericseal 175 may not be greater than about 2%, about 5%, about 8%, about10%, about 15%, or about 20%.

In some embodiments, force concentrator pattern 300 may not becontinuous across frame 170. For example, force concentrator patter 300may include separated portions at the corners of frame 170. For example,as shown in FIG. 10, corner portions 310 may be similarly raisedsurfaces added to frame 170 as a part of force concentrator pattern 300.Corner portions 310 may be generated by chemically etching or machiningframe 170 in the same manner as force concentrator pattern 300. Cornerportions 310 may have the same thickness as that of force concentratorpattern 300. In some embodiments, the surface area of force concentratorpattern 300 may be reduced by adding corner portions 310 to frame 170.In some embodiments, corner portions 310 and force concentrator pattern300 together allow the compressed area of frame 170 and the sealingsurface 175 to be approximately constant, and thus the compressivepressure to be generally uniformly or evenly distributed across frame170.

In some embodiments, force concentrator pattern 300 may be formed inpolymeric seal 175. For example, polymeric seal 175 may have a largerthickness across force concentrator pattern 300 and a smaller thicknessacross other areas. In some embodiments, force concentrator pattern 300may be an integral part of frame 170 and/or base 180. In someembodiments, force concentrator pattern 300 may be on a selected surfaceor both surfaces of frame 170 and/or based 180. In some embodiments,each EHC cell in an EHC stack may have force concentrator pattern 300.

In some embodiments, the use of force concentrator pattern 300 mayreduce the requirement for the amount of compressive load applied toframe 170 and base 180. The reduced requirement for the compressive loadmay allow reduced requirement for the materials of frame 170 and base180, which may allow for a wide selection of materials to be used forframe 170 and base 180. In some embodiments, frame 170 and base 180 maybe formed of the same materials or different materials. Frame 170 andbase 180 may be formed of a metal, such as, stainless steel, titanium,aluminum, nickel, iron, etc., or a metal alloy, such as, nickel chromealloy, nickel-tin alloy, Inconel, Monel, Hastelloy, or a combinationthere of. In some embodiment, frame 170 may also be formed of polymers,composites, ceramics, or any material capable of handling thecompressive load, force, and/or pressure applied to the EHC cell or EHCstack upon assembly.

In some embodiments, frame 170 and base 180 may include a clad material,for example, aluminum clad with stainless steel on one or more regions.Cladding may provide the advantages of both metals, for example, in thecase of a bipolar plate fabricated from stainless steel-clad aluminum,the stainless steel protects the aluminum core from corrosion duringcell operation, while providing the superior material properties ofaluminum, such as, high strength-to-weight ratio, high thermal andelectrical conductivity, etc. In some embodiments, frame 170 may includeanodized, sealed, and primed aluminum. In some embodiments, frame 170may include chromated and spray coated aluminum.

In some embodiments, frame 170 may be formed of a composite, such as,carbon fiber, graphite, glass-reinforce polymer, and thermoplasticcomposites. In some embodiments, frame 170 may be formed of a metal thatis coated to prevent both corrosion and electrical conduction. Accordingto various embodiments, frame 170 may be generally non-conductive,reducing the likelihood of shorting between the electrochemical cells.Base 180 may be formed of one or more materials that provide electricalconductivity as well as corrosion resistance during cell operation. Forexample, base 180 may be configured to be electrically conductive in theregion where the active cell components sit (e.g., flow structure, MEA,etc.).

Factors and properties to be considered in selecting the material andgeometry for a component (e.g., polymeric seal 175, first seal 230,second seal 240, third seal 250, frame 170, and base 180) may include atleast the design of force concentrator pattern 300, compressive loadrequirements, material compatibility, sealing pressure requirement, costof material, cost of manufacturing, and ease of manufacturing. Thevariety of materials made suitable by force concentration pattern 300described herein may allow for the selection of less expensive materialsand less costly manufacturing. For example, lower cost commodityplastics, some of which have been listed herein, may be used for thepolymeric seals (e.g., polymeric seal 175, first seal 230, second seal240, and third seal 250). In addition, multi-component bipolar platescould be expensive to manufacture due to the intricate details on theplates requiring the use of expensive conventional milling. Utilizingthe polymeric seal 175 and force concentrator pattern 300 as describedherein may reduce the cost and complexity of the manufacture of bipolarplates 150 and 160. For example, frame 170 and base 180 may bemanufactured together with force concentrator pattern 300, which mayreduce the thickness of bipolar plates 150 and 160, manufacturing cost,and manufacturing complexity by allowing the use of polymeric seal 175and generally uniform distribution of compressive pressure along thesealing surface of polymeric seal 175.

It is understood that the features described herein may be used to sealother components of the electrochemical cell and/or may be used in cellsthat do not employ the cascade seal configuration.

Other embodiments of the present disclosure will be apparent to thoseskilled in the art from consideration of the specification and practiceof the present disclosure herein. It is intended that the specificationand examples be considered as exemplary only, with a true scope andspirit of the present disclosure being indicated by the followingclaims.

What is claimed is:
 1. A bipolar plate assembly, comprising: a frame and a base, at least one of the frame and the base having a shape of a force concentrator pattern or having a first surface comprising a force concentrator pattern, the force concentrator pattern comprising a raised surface extending partially across the first surface; wherein a surface area of the force concentrator pattern across the length of the frame or the base is generally constant, thereby producing a uniform compressive pressure along the length of the frame and/or the base when the bipolar plate assembly is under compression.
 2. The bipolar plate assembly of claim 1, wherein the surface area of the force concentrator pattern across the length of the frame or the base ranges from between about 2 cm²/cm to about 10 cm²/cm.
 3. The bipolar plate assembly of claim 1, further comprising at least one seal assembly between the frame and the base.
 4. The bipolar plate assembly of claim 3, wherein the seal assembly is an elastomer seal or a polymeric seal.
 5. The bipolar plate assembly of claim 3, wherein the compressive pressure on the seal assembly is generally evenly distributed across the seal assembly when the bipolar plate assembly is under compression.
 6. The bipolar plate assembly of claim 1, wherein the frame and the base are two pieces coupled together or are one integrated part.
 7. The bipolar plate assembly of claim 6, wherein at least one of the frame and the base is laminated with a polymeric material or coated with a polymeric film on a top surface and/or a bottom surface.
 8. The bipolar plate assembly of claim 7, wherein the compressive pressure on the polymeric material or the polymeric film is generally evenly distributed across the frame and/or the base when the bipolar plate assembly is under compression.
 9. The bipolar plate assembly of claim 2, wherein the bipolar plate assembly is at least one of a plurality of bipolar plate assemblies forming an electrochemical stack.
 10. The bipolar plate assembly of claim 2, wherein the compressive pressure ranges from 5,000 psig to 40,000 psig.
 11. The bipolar plate assembly of claim 2, wherein the force concentrator pattern has a thickness ranging from 0.025 mm to a thickness of the frame and/or the base.
 12. The bipolar plate assembly of claim 2, wherein at least one of the frame and the base has a second surface comprising the force concentrator pattern.
 13. A method of assembling a bipolar plate assembly, comprising: compressing a frame and a base of the bipolar plate assembly, at least one of the frame and the base having a shape of a force concentrator pattern or having a first surface comprising a force concentrator pattern, the force concentrator pattern comprising a raised surface extending partially across the first surface, wherein a surface area of the force concentrator pattern across the length of the frame or the base is generally constant, thereby producing a uniform compressive pressure along the length of the frame and/or the base when the bipolar plate assembly is under compression.
 14. The method of claim 13, wherein the surface area of the force concentrator pattern across the length of the frame or the base ranges from between about 2 cm²/cm to about 10 cm²/cm.
 15. The method of claim 13, wherein the bipolar plate assembly comprises at least one seal assembly between the frame and the base.
 16. The method of claim 15, wherein the seal assembly is an elastomer seal or a polymeric seal.
 17. The method of claim 15, wherein the compressive pressure on the seal assembly is generally evenly distributed across the seal assembly when the bipolar plate assembly is under compression.
 18. The method of claim 15, wherein the compressive pressure on the seal assembly is greater than the yield strength of the material of the seal assembly.
 19. The method of claim 13, wherein the frame and the base are two pieces coupled together or are one integrated part; wherein at least one of the frame and the base is laminated with a polymeric material or coated with a polymeric film on a top surface and/or a bottom surface; and wherein the compressive pressure on the polymeric material or the polymeric film is generally evenly distributed across the frame and/or the base when the bipolar plate assembly is under compression.
 20. An electrochemical cell comprising: a pair of bipolar plate assemblies and a membrane electrode assembly located between the pair of bipolar plate assemblies, wherein at least one of the bipolar plate assembly comprises: a frame and a base, at least one of the frame and the base having a shape of a force concentrator pattern or having a first surface comprising a force concentrator pattern, the force concentrator pattern comprising a raised surface extending partially across the first surface, wherein a surface area of the force concentrator pattern across the length of the frame or the base is generally constant, thereby producing a uniform compressive pressure along the length of the frame and/or base when the bipolar plate assembly is under compression. 